Lead apparently caused an overwhelming amount of social pathology at global scale in the 20th Century. The peak of this catastrophe occurred ~1994 when homicide rates in some urban American inner city environments approached 1%: Total social collapse.
Now that tetraethyl lead has been removed from car gasoline, blood lead levels have declined to values never before seen; along with these super low lead levels we are now experiencing super low crime rates as well as several other socially important outcomes in youth cohorts. One mechanism of action of lead relates to brain damage to the executive functioning part of the brain which controls impulse control. Without functioning impulse control one would expect civilization to collapse (as happened in the last quarter of the 20th Century). Lead has been a known neurotoxin for thousands of years. The CDC considers there to be no safe level of lead.
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Edited by mag1, 01 September 2022 - 09:54 PM.